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Can airline pilots communicate with dispatchers?
Is it possible for airline pilots to communicate with dispatchers? If so, what methods do they use? A special radio channel?

Yes, and it is a regulatory requirement that it is so.

§121.99   Communications facilities—domestic and flag operations.
(a) Each certificate holder conducting domestic or flag operations must show that a two-way communication system, or other means of communication approved by the FAA certificate holding district office, is available over the entire route. The communications may be direct links or via an approved communication link that will provide reliable and rapid communications under normal operating conditions between each airplane and the appropriate dispatch office, and between each airplane and the appropriate air traffic control unit.

The typical way to contact dispatch is through SELCAL which allows two way communications between two specific parties over HF or VHF radio.  To contact a dispatcher we would tune the COM associated with SELCAL to the proper frequency (these were charted on company airport pages and you would use one from an airport nearby that you are overflying) and then use our handheld microphone (with keypad) to dial a code for our dispatcher, which is noted on our release paperwork.
As long as you are monitoring a SELCAL frequency and dispatch (or someone else with your aircraft code) calls you, the airplane will announce "SELCAL" and typically a light or some other visual notification will come on.
Once connected, you talk to your dispatcher over that com radio the same as you would talk to ATC.  From there your dispatcher can connect you to maintenance, med link, or anyone else you might need to talk to.
For larger airplanes typically used on overwater routes you will probably also find a satellite phone in the cockpit that can be used as an alternative way to call dispatch.
Textual communications to and from dispatch are also possible using ACARS.

Umm, don't you mean ARINC?  SELCAL is used to alert pilots that ATC wants to talk to them on HF so that they don't have to listen to the static....

@Lnafziger That is one use for SELCAL, but not the only. We used it to call directly to our dispatchers desk (it rang on their phone, and they could call us the same way).  For us, SELCAL used the second VHF com radio (we had 3 VHF and no HF comm).

@Lnafziger as I recall I think we could also do ARINC phone patches through an operator, but I'll have to dig out my manuals to recall the specifics.

The two 747 carriers I worked for used Stockholm Radio for HF communications between aircraft and dispatchers, and they could SELCAL us. Individuals could also set up an account by supplying Stockholm Radio with credit card information. They would give you an ID number to use when contacting them. I used to occasionally call my spouse this way. Remember, though, open water, especially calm water, soaks up HF energy, so HF usage in the South Pacific was always a problem.

@Terry -- are you talking about groundwave or skywave HF comms?  Because I'd think that you'd have no problem reaching well, almost anything you wanted on HF if you knew how to work the skip...amateur radio operators routinely work transoceanic in their HF bands using skywave techniques.

@UnrecognizedFallingObject On the equipment we were using, all we could do was select a frequency. We had no ability, equipment wise, to 'work the skip'. All I can report is what the practical effect was for the equipment we had. If lightning was in the area, every discharge created heavy static. Precipitation in general caused problems. At altitude in cirrus clouds, the build up of static electric on the airplane also often caused a loud squeal. Typically back then it was the f.e.'s job to find a workable frequency. No sat com ability on those old airplanes.


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Can a CFI give required instruction and endorsements on a 3rd class medical?
Let's suppose a CFI can no longer qualify for a 1st or 2nd class physical, or maybe her/his 2nd class physical was 18 months ago. Can she/he still give required instruction and endorsements as long as they don't charge for their time and are not paid for it in any other way?

A CFI with a third class medical can provide any kind of instruction that they are qualified for (and be compensated for it), per 14 CFR 61.23(a)(3)(iv) and (v). The FAA's position in these scenarios is that you're being compensated for the transference of knowledge, not the operation of the aircraft.
For completeness, A CFI can provide instruction WITHOUT a medical if they are not flying PIC or acting as a required crew member. In this scenario training can be provided for certain additional ratings (e.g. commercial) or flight reviews AS LONG AS the student can PIC during that flight AND the CFI is NOT a required crew member (i.e. safety pilot for insturment training).  Additionally, the FAA has made a legal interpretation that a CFI can provide instruction to a pilot that is not current to carry passengers, as long as all other requirements for the student to be PIC can be met.
The specific regulations that allows this are 14 CFR 61.3(c)(2)(viii) and 14 CFR 61.23(b)(5)

A CFI can give, and charge for instruction with a 3rd class medical.  If the training does not require the CFI to be PIC, then the instruction can be given (and charged for) with no medical at all.

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What is the concept behind being able to continuously pour iced tea while rolling an airplane?
I recently saw Bob Hoover's famous video in which he is pouring tea while he is rolling the plane. Can you explain the physics that allow the tea to flow "up" when the plane is upside-down? Why doesn't the tea fall out of the pitcher like it would normally if turned upside-down?

See here for the solution: http://aviation.stackexchange.com/questions/489/is-it-safe-to-roll-an-airplane-that-isnt-approved-for-it

Hi.  Welcome to SE.Aviation!  Please post a link to the video.  My guess is that he performs a barrel roll in which case, the force you feel is always towards the floor of the aircraft.  If you closed your eyes, you would not even know that you were rolling.

Can u please explain how the force is always towards the floor?@simon

You're better off asking on SE.Physics, but what happens when you tie something to the end of a piece of string and whirl it around your head?  Centripetal force you seek.

Have you ever been in a rollercoaster, or a fast-maneuvering car?

I'm voting to close this question as off-topic because it belongs to physics.se.

Also: Does centrifugal force exist?

The maneuver Bob Hoover is performing is a specific kind of roll called a barrel roll.  If you look at the path traced by this maneuver it is a corkscrew rather than a linear path that you might be imagining.  Because the airplane is rotating about a longitudinal axis as it translates forward there is centripetal acceleration toward the axis of rotation, or "up" in the reference frame of the person in the airplane.
To the observer in the reference frame of the airplane (e.g. the pilot or a passenger), the centripetal acceleration is interpreted as the fictitious centrifugal force.  This is exactly the same mechanism that you experience when driving around tight curves, though the force is in a different direction.  The end result in the airplane is that for a properly executed barrel roll, the centripetal acceleration causes the net force you experience inside the airplane to remain constant throughout the roll (in your reference frame, with the net force pointed "down").
If you were to close your eyes you would not know the plane rolled.  Likewise, the iced tea does not "know" it is upside down.  For a less dramatic demonstration, next time you are on a commercial airplane pay attention to when the plane is banking and turning and note that a cup of water on the tray doesn't notice the turn.  The cup stays in place and the fluid remains level (with reference to the airplane).
You can also demonstrate this with a small bucket and some rope.  Put some water in the bucket, tie the rope to the bucket and swing it in a circle vertically (be careful).  The water stays in the bucket if you swing it fast enough, and this is the same mechanism you see in Bob Hoover's video except it is the whole airplane being swung around in a circle like the bucket.

so we can say that the G force applied by aircraft's floor is more than that of earth's

@RocK. Gravity is stil pulling you, in exactly the same direction with exactly the same force.  The floor exerts a force opposite to the centripetal force.  So gravity is pulling you down with +1g, centrifugal force is applying a force on you to push you away from the centre of the roll.

You must fly different airlines to me... The last plane I was on, the cup certainly didn't stay still! Hopefully it was just the copilot practicing his coordinated turns

For the net force to be constant, would not the centripetal acceleration have to be 2g higher at the top of the roll than at entry and exit? I think that would lead to either a noticeably pear-shaped barrel ( narrow end up) or require an airplane capable of accelerating significantly from entry to the top, and correspondingly able to lose all the excess speed on the way down. From the film I have seen, Bob Hoover's 707 roll appears to be somewhat pear-shaped, though it is hard to tell if the camera is panning.

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How does push forward work?
From Facebook video shows a BA aircraft being pushed forward into a hangar. I wonder how it works? Do they rotate nose wheel 180 degree to push it or there is attachment point for the tug to push forward?

Does this answer your question? Is it common for aircraft tugs to work from under the aircraft?

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What are the pros and cons of vacuum and pressure gyros?
Inspired by this question, I would like to know what the pro's and con's of the mostly used vacuum-gyro and the less used high-pressure-gyro is.
Side-question: Are there any other ways to make the Artificial Horizon work?

Definitely other ways, yes. For example, the old electric spinning gyros, or the new solid state electronic gyros that are taking over the market.

Inspired by this question, I would like to know what the pro's and
  con's of the mostly used vacuum-gyro and the less used
  high-pressure-gyro is.

It is largely related to the instruments in your aircraft but in reality its all about air pressure and the systems are really doing the same thing in the end of the day.
Lets look at the evolution a bit, early aircraft that lacked an electrical system generally used a small external venturi to generate low pressure suction for the early gyro instruments. Note the venturi tube in front of the door about half way up the body on this early Cessna 170.

(source)
Since it was easy to generate low pressure this way early instruments were built as suction based. As planes got faster and external (drag educing) things were removed these systems went internal. Since the instruments were already suction based it was logical to make engine (or electrical) suction pumps to drive them.
When pumps moved into the engine compartment they came with some issues. Wet suction pumps have an oil issue that can seep into the system and cause issues with the instruments. That was solved with the advent of the dry pneumatic pump however that was a bit more susceptible to debris clogging but could provide both positive and negative pressure.
This paper outlines both systems as well as their pros and cons in depth and answers the question quite well. However the end result is that both systems provide the same outcome and in the view of the instruments there is no real difference.

Gyro Instruments Within the case of the gyro instrument the air flows
  through the air seals of the gimbalsʼ bearings and across the rotor,
  spinning the rotor on its axes. The exhausting airflow from the rotor
  housing applies precession forces to maintain a reference to earth in
  the attitude gyro and the attitude of the aircraft in the directional
  gyro. The mechanics of the gyro instrument remain the same, whether it
  is driven by the airflow in a pressure or vacuum system. The air- flow
  through the instrument is a result of the differential pressure
  between the instrumentʼs air inlet and the air outlet ports. In a
  vacuum system the pressure at the air outlet port is lowered below
  atmospheric pressure. The differential pressure between the atmosphere
  and the pump now forces air to flow through the instrument. In a
  pressure system the pressure at the air inlet port is raised above
  atmospheric pressure and the airflow is in the same direction.

So what are some pros and cons,
In a vacuum system the filter is upstream and air is pulled through it and it does a good job of keeping the air clean.

...filtering the air entering the instrument. This filter will remove
  most contaminates from the air, but moisture is not one of them.
  Periodic replacement of this filter will ensure clean airflow through
  the instruments.

While in pressure based systems the air filter is generally mounted in line but has a similar effect

In a pressure system there is an inline filter in the line between the
  outlet port of the pump and the inlet port of the gyro instrument.
  This restricts, but does not completely stop, the flow of all
  contaminates to the instrument.

However pressure systems have a moisture problem since the compression of air creates moisture, this may add moisture while a suction system will only draw ambient moisture.

Unfortunately when air is compressed, moisture is created. Although
  the pressure is extremely low (approximately 2.5 to
  4.5 PSI), this system is no exception. Moisture is the No. 1 contaminate, contaminating the gyro bearings in a pressure system.

The paper also outlines that both systems are susceptible to downtime due to pump inspections and system maintenance. Which is a con of both systems.

Side-question: Are there any other ways to make the Artificial Horizon
  work?

Yes, electricity

(source)

Another view of Venturi tubes.

You might add that the failure mode for some vacuum pumps / compressor may send a lot of debris out with the compressed air. When that is the case, a vacuum system protects the expensive instruments better compared to a pressure system. Debris in the engine department is less expensive compared to debris in the instruments.

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Could a private pilot violate 'commercial' rules if there is no compensation or expense sharing at all?
How might a private pilot run into regulatory trouble by flying a passenger if they don't receive any compensation at  all? I'm interested in some specific scenarios. In all of these cases, let's assume the pilot receives no compensation of any kind, and pays all costs himself. The passenger makes no contribution whatsoever. There are no exchanges of services, no favours, no under-the-table deals. Also assume that none of the activities mentioned are in any way concerned with the employment or other business activities of either pilot or passenger.

The pilot flies the passenger somewhere the passenger wasn't planning on going, but nonetheless enjoys. I'm assuming this is not a problem, and happens most days
The pilot flies the passenger to visit a family member, one they wouldn't have visited otherwise.
The pilot flies the passenger to a recreational event, which they are attending.
The pilot flies the passenger to a recreational event, which only the passenger is attending.

Again, no money changes hands, no compensation of any kind, pilot pays all the costs.
US regulations. And please, specific citations of cases or regulations.
EDIT: Since this appears to be a source of confusion, let me repeat for the third time in the question: there is no compensation or expense sharing and nothing of value changes hands. The pilot pays all costs, at exactly the same rate as he would if he was flying alone. There is no 'goodwill' expected, no future business deals, nothing.

When you say no compensation of any kind, are you familiar with, and referring to, the FAA's broad definition of compensation, or specifically monetary compensation?

I don't know the details of it, but I mean no compensation at all. The passenger pays no part of the costs, no expenses, no contributions in kind and no under-the-table deals. If you have a specific form of compensation in mind that I might not have thought of, please feel free to mention it.

The FAA also considers other broad reaching things compensation, like possible good will that the flight may encourage in the passenger (I.e. you do them a favor, so they may do one for you in the future.)  It's probably worthy of a question of its' own, if it hasn't already been asked, but is why I wanted to know if you were intending to exclude other "non-traditional" forms of compensation that some people may not be aware of.

Yeah what @Lnafziger said!  Many of these ambiguous regulations are there so the FAA can decide when they think you're doing something they don't like.  Lay low and don't do anything obtuse. Don't draw attention to yourself and normal human-being things like having someone buy you a meal for flying with them will never be noticed.  Strictly one guy's opinion.

I understand that everybody keeps asking this, but I really mean no compensation at all.

@DJClayworth I think you're looking for a black and white answer here, but in fact the FAA is operating on the principle that "I know it when I see it" and the vague definition of compensation gives them enough leeway to do that. They have to balance a pilot's right to get utility from his own vehicle with the need to protect the public from unqualified pilots; their assumption is that most people have no way to assess whether a pilot is competent and an aircraft is safe. If they defined compensation precisely, then people would work around that definition. People are clever that way :-)

Everything but #3 is a charter, money or not.  Flight time = compensation.

@acpilot. Do you have cases or judgements to back that up?

Off the top of my head: read the FAA's Haberkorn opinion and Bobertz opinion. Google "FAA Haberkorn" and "FAA Bobertz." Also, the FSDO can only give you their take on a particular scenario. Basically amounts "yeah...we'd probably violate you for that." FAA chief councel's opinion actually matters and if you want real, authoritative answers (policy) you should go straight to them for answers.

It seems that the "logging of flight time" part would apply if it were an actual benefit that you would not otherwise receive.  I.e. if someone provided an airplane for you to fly in exchange for you taking them somewhere.  Otherwise, if you are paying all costs anyway and could have flown the aircraft without them without there being any difference in cost (or the logging of flight time), then I don't see how that could be considered compensation.

The issue is not compensation. The issue is common purpose. If no common purpose exists then 61.113 does not apply and the quantity and method of compensation is irrelevant. 61.113 is only worth talking about once common purpose is established. Until you have CP the flight is a charter and you need a 119 certificate. The answer to the OP's question is: ILLEGAL for 1, 2, and 4 for sure.

@acpilot Can you actually point to decisions, cases or judgements that back that up? Neither Haberkorn nor Bobertz apply here because they both involve expense sharing. Feel free to join chat: http://chat.stackexchange.com/rooms/44430/discussion-between-djclayworth-and-ymb1

@acpilot I'm not disputing that.  However, there have been a lot of comments in this Q&A stating that logging of flight time IS considered compensation (without specifying any exceptions, and seemingly applying it when it doesn't seem to be appropriate).

Let's dicuss this in chat. Link above.

No.  Without compensation, a private pilot cannot violate 'commercial' rules.
For starters, the FAA considers the ability to log flight time as compensation.  A legal interpretation to John Harrington issued October 1997 clarifies that point.  The regulation that you are asking about is quoted below.

§ 61.113   Private pilot privileges and limitations: Pilot in command.

(a) Except as provided in paragraphs (b) through (h) of this section, no person who holds a private pilot certificate may act as pilot in command of an aircraft that is carrying passengers or property for compensation or hire; nor may that person, for compensation or hire, act as pilot in command of an aircraft.

An interpretation to Mike Sommer in part says

The FAA construes the terms “compensation for hire” very broadly. It does not require a profit, profit motive, or the actual payment of funds. Instead, the FAA views compensation as the receipt of anything of value. In an interpretation letter to John W. Harrington, from Donald Byrne, Assistant Chief Counsel, October 23, 1997, it is stated that, “any reimbursement of expenses (fuel, oil, transportation, lodging, meals, etc.), if conditioned upon the pilot operating the aircraft,’ would constitute compensation.”

In 1985 the FAA chief counsel determined that there had to be a bona-fide common purpose in conducting the flight.  See the Chero Interpretation from December 1985.

Section 61.118(b) allows a private pilot to share the operating expenses of a flight with his or her passengers. Additionally, the FAA has interpreted 61.118(b) so that the only allowable share-the-costs operations are those which are bona fide, that is, joint ventures for a common purpose with the expenses being defrayed by all passengers and the pilot. Nor does Section 61.118 permit pilots who want to build up time toward their commercial pilot certificates to carry expense sharing passengers to a destination at which they have no particular business. (emphasis added)

To answer your question.

The pilot flies the passenger somewhere they weren't planning on
going, but nonetheless enjoy. I'm assuming this is not a problem,
and happens most days.
There is no problem here.  The pilot would pay for the expenses of the flight anyway so taking a passenger is OK.

The pilot flies the passenger to visit a family member, one they wouldn't have visited otherwise.
This is legal if the pilot pays for all expenses.  Since the FAA has determined compensation quite broadly I would expect they would also consider food and lodging as compensation as stated previously in a legal interpretation.  The pilot would, for all practical purposes, pretend the passenger was not there and make their own arrangements.

The pilot flies the passenger to a specific recreational event, which they are attending.

This is legal and the pilot can share the costs with the passenger.

The pilot flies the passenger to a specific recreational event, which only the passenger is attending.
This goes back to #2 above.  The pilot does not have a bona-fide common purpose for making the flight.  They cannot accept any compensation in any form for the flight to be legal.

I have never seen a case where 'flight time as compensation' has been applied to a flight without there being sharing of expenses. Feel free to point me at one if you know of one.

See chat: http://chat.stackexchange.com/rooms/44430/discussion-between-djclayworth-and-ymb1

@ymb1 This only applies if you're splitting costs, right? If the pilot is paying the full costs of the flight (as specified in the question,) then it seems that the answer is always no. After all, the pilot is not getting any extra hours any more cheaply than they would had the passengers not been present. The passengers get free transportation, but the pilot gets nothing he couldn't have gotten by simply flying himself around for the same duration. So, I agree with DJ that the answer should actually be 'No' if the pilot is indeed paying all expenses associated with the flight.

Yeah "Flight time you pay for yourself, and happen to take a passenger" is not compensation. The "Flight time as compensation" only applies where the cost is being reduced for the pilot: eg the passenger is paying the rental, fees, or gas etc. Otherwise the pilot is simply flying somewhere and gaining nothing they wouldn't have anyway.

Even in the event that the passenger contributes to cost sharing, common purpose can be established by nothing more than their mutual decision to fly together.  One's relative level of enthusiasm isn't part of the equation.


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Does weight of an aircraft affect its ability to pull G?
This question includes the quote:

A C42 doesn't weigh much, so to pull the 5+ G required to exceed the design specifications of it's wing spar and fixings would require extreme speeds.

I'm not an aircraft design expert, but it seems to me that the weight of a plane doesn't affect its ability to pull G (in a maneuver, not sustained). With sufficiently large control surfaces and a good amount of power a light aircraft would find it easier to pull G than a heavy one. Am I wrong?

You may get a different answer if you're considering  nearly instantaneous loading, or the ability to sustain (like, in level flight) a particular G loading. May be worth clarifying that.

It depends more on the wing loading $W/S$. A sustained turn might be a good way to illustrate it, let's see if someone feels like elaborating a proper answer.

Well, lighter and smaller tolerates more G's.  Radio-controlled pylon racers and dynamic-soaring sailplanes weighing 20 to 40 pounds commonly pull over 40 G's.

@CamilleGoudeseune Is that because it doesn't really matter if they break up in flight? And there isn't crew to die a horrible squishy death?

This is an outstanding question.  In the simplest case:  attach a rubber band to a very light object and to a very heavy object and pull.  Which case does the rubber band break?  Given that the  wing generates the same amount of pulling force at stall AoA,  which is more stressed, the light plane wing structure or the heavy?  It is indeed a comparison of pitch rate vs acceleration, which could lead to a review of the V maneuvering speed concept.  I'm seeing (with full scale aircraft) perhaps a greater G peak with greater pitch rate (for lighter aircraft).  Validation would be interesting

But must we multiply G load by Weight to get Actual stress load on the wing spar (assuming that's what fails when "G loads" are exceeded)?

Since recreational aircraft weights do not vary nearly as much as large cargo carriers, it would be great if some one with 747 airliner experience could share what their POH said about V maneuvering speeds and "G limits".

@DJClayworth Yes, the stakes are lower, and what's onboard is less squishy, but the motivation to survive the maneuver abides.

Firstly there is the square-cube law. Smaller objects handle higher g-forces (half the size = 1/8 the mass = twice the max g-force). Also, a given plane will definitely will tolerate higher g-forces if there is less fuel and cargo. But comparing a less robust vs more robust design of the same size is tricky: it is stronger but heavier, and these act in opposition.

Hey, thanks for linking to my original question :)

Any source that does not know how to use "its" and "it's" correctly is untrustworthy.

@KevinKostian. Please write your comment as an answer.  We really have a good discussion here about the effects of inertia on both rate of pitch and acceleration (to the new direction) from a maneuver control input.  I think the gust case favors the light plane and the maneuvering case has pros and cons.  Would love to see data.

The reason RC aircraft can pull such loads is the square-cube law.  The weight cost of components that can stand the stresses is quite low.  The bigger the plane the greater the percent of it's total mass is devoted to keeping it from breaking.  The RC also must be built stronger because of the handling loads.  Try picking that jetliner up by it's tail and see what happens to it.

This question would appear to be like asking "does the weight of a car affect its speed" ?  That is a very complicated issue.  The Veyron is the fastest car.  It's heavy.  Land-speed-record type cars are extremely heavy.   If you take a car and make that car lighter, it will go faster.  However to take a car and make it faster, you almost always have to make it heavier (add a turbo unit, add more sophisticated wings or suspension, add stronger frames, much bigger batteries, etc etc).  I'm not even sure what the question means!

Statistics give a different picture: Smaller airplanes usually have lower wing loadings and higher G limits than heavier, larger ones. But the short answer is: You are right and the reasoning in the quote is wrong.
Now let me first get some things clarified:

Weight is mass times acceleration, mostly gravitational but also centrifugal acceleration. Weight is therefore a force. From here on, I will interpret your question as "does wing loading of an aircraft affect its ability to pull G?", wing loading being mass per reference area.
You can either fly multiple gs by maneuvering or by flying into gusts. Both need to be looked at separately.

Now to the first way of pulling Gs: Tight circles. If we don't care about height loss (instationary turns), the g limit is a design factor and independent of wing loading. Lighter airplanes require less speed to reach their G limit, so the quote is wrong. Less speed is required.
The stick force for pulling Gs goes up with the stability margin and dynamic pressure. Higher wing loading, therefore, will require more sick force, all other things being equal. The large control surface helps to reach the G limit with maximum forward CG. Installed power will limit the height loss in instationary turns, so both help to reach the G limit.
If you want a light stick force to pull maximum Gs, fly with a rear CG location and light wing loading. If we consider stick forces to be a factor, a low wing loading helps to reach high Gs.
Now for the gust case: Here, gust strength and flight speed determine the G load. Given again two identical planes which differ only in wing loading, the heavier one needs to fly faster, so the same gust will result in a lower angle of attack change from flight into a vertical gust and a lower gust load factor compared to the lighter plane. Make no mistake: The structural stresses will be higher for the heavier airplane, but its higher mass requires proportionally more lift for the same G loading. With the speed ratio between flight speed and gust speed lower for the heavier airplane, it will experience less Gs.
Ergo: In the gust case a lighter wing loading will result in higher Gs. Which also explains why lighter planes have higher G limits. Another explanation are scaling laws: Larger airplanes will have higher wing loading.

P.S. Someone felt that the g needs to be a capital G. Normally, the gravitational acceleration is denoted with a lowercase g, but maybe using the capital G improves readability. Also, I normally don't put an apostrophe between a word and a plural s, but even SE seems to succumb to Internet spelling, so I leave it at that.

Re: "The g limit is a design factor and independent of wing loading". It is not always the case. G-limit usually decreases as gross weight is increased above a certain threshold in the same aircraft. When the aircraft is light enough, with minimal fuel or stores, then the g-limit can stay relatively the same. This decrease in g-limit with increasing weight is seen on aircraft such as F-15, F-16, F-18 and Su-27.

@LJQCN101 My focus is on smaller airplanes. Of course, if you add supersonic planes and types which dump 15% of their take-off mass in one instance, things become more complicated. Remember, this started with the Ikarus C42 ultralight.

Sure but not only supersonic planes, as there’re plenty of manuals out there, and one thing in common is that both g-limit for maneuvering and gust takes weight into account. The maneuvering g-limit can be constant for a ranges of weight, as I said above. I’ll be adding other aircraft if people need it.

@LJQCN101 It's not so simple. Much depends where the weight is. Fuel in tip tanks has a different influence than bombs in a central bomb bay. Please don't assume I don't know this, but I wanted to keep the answer on point.

@LJQCN101 You will see this with reversible control when a combination of forward cg and high gross weight means too high stick forces to pull out of a dive. Not all airplanes use hydraulic control systems!

I thought maybe our interpretation of ‘g-limit’ was a bit different, so I’d like to rephrase my reply. I was not talking about the attainable / available load factor by the pilot or aerodynamically by the aircraft, as I’m not denying or neglecting any of the factors that could contribute to it. I was talking about the load factor that the aircraft structure is designed to tolerate, and whether weight or wing loading has any impact on it. I expressed my observations from aircraft manuals and that’s it.

Short answer: A heavier weight, by loading more fuel or stores, decreases the ability of the same aircraft to pull more instantaneous Gs (available load factor) aerodynamically.
The load factor in the direction of Lift can be calculated as:

n = (Total Lift + Thrust * sinα) / Weight

So with a heavier weight, you'll need a higher lift (e.g. by increasing AOA), and/or a greater thrust, to achieve the same load factor.
For an example, you can refer to the F-16C/D SUPPLEMENTAL FLIGHT MANUAL T.O. GR1F-16CJ-1-1, linked https://publicintelligence.net/hellenic-air-force-f-16cd-flight-manuals/
In the 'Available Load Factor' chart at Figure A1-8 (block52) or Figure B1-8 (block50), where there's clearly an entry for GW (gross weight). A heavier weight leads to a lower attainable G for the same condition.

Regarding the pilot observed / designed / allowable G-limits, it also takes gross weight into consideration, as the wing is designed to withstand a certain amount of force. For a simplified force analysis, you can assume the force is in the body Z axis, so the wing withstands a force of Nz*weight, where Nz is the normal load factor.
Just to be sure, load factor in the lift direction (stability Z axis) is not to be confused with normal load factor (Nz), which is in the body Z axis:

Nz = Total Normal Force / Weight = (Total Lift * cosα  + Total Drag * sinα) / Weight

So here, Nz takes into account the lift and drag components in the body axes, while load factor takes into account the thrust component in the stability axes.

The G-limit of F-16C, versus gross weight:

The maneuver and gust G-limits of B-52H, versus gross weight:

Actual load on the wing spar will be G load × weight, not just G factor.

@RobertDiGiovanni To be specific, the actual force that is perpendicular to the wing is the normal force in the body Z axis, which equals to Nz*weight, or (Total Lift * cosα  + Total Drag * sinα). Nz is normal load factor, not any other factors.

That's right.  That's how hard the wing is tugging on the fuselage.  I think this is why some folks switched to Newtons.  In this case, G and mass change, resulting in the same (instantaneous) load on the spar!  (Even though the pilot will experience higher G if the plane is lighter.

The crux of the analysis seems to be the potential change in angle of attack from a straight and level flying condition (though other conditions are possible).
All aircraft have a limit in their flight envelope where an abrupt change in angle of attack, from maneuvering or change in relative wind from a gust, can cause either a stall or G forces exceeding the aircraft limit.
Below this maneuvering speed, AoA can increase until the aircraft stalls without exceeding G limits.
Because the AoA required for adequate lift is lower in lighter aircraft, there is more "room" to increase AoA before stall.  Within the range of AoA before stall, the relationship of lift to AoA is more or less linear.
So, a lighter aircraft producing 1 G at 3 degrees AoA can produce 5 G at 15 degrees AoA before stalling (if the stall AoA of that particular airfoil is 15 degrees).
The same aircraft with more weight might need 6 degrees AoA at the same speed or 3 degrees at a higher airspeed.
Working at the same speed, we see that the heavier aircraft can only produce 2.5 G before reaching its stall limit.
Crucial to understanding all of this is that an extremely light aircraft, like a paper airplane, can change directions more rapidly than it can increase AoA.  Not so with heavier aircraft.
So, now it boils down to rate of pitch vs rate of change in direction.
The lighter airplane, with the same control input, at the same speed, has less inertia to overcome.  It can pitch faster$^1$ than the heavier one!
Asking the question about ability to pull G "in a maneuver, not sustained" put us on the right track, as this, by virtue of the change in AoA, is where the greatest G forces are found.
More reading here.
$^1$ Peter Kampf also pointed out moving CG back has the same effect: " lighter stick forces "

Realizing the heavier aircraft weights 2x more, therefor the load on the wing would be the same with equal pitch rate!

A heavier aircraft does not immediately equal to a lower pitch rate. As told in NASA TP-1538, the component of aircraft pitch acceleration can be calculated as: pitching moment coefficient Cm * dynamic pressure * mean air chord * reference wing area / moment of inertia Iy. As you can see, increasing Cm by e.g. reducing static margin, can make up for the increased Iy. But the ability to pull G is more related to CL than Cm, due to how load factor is calculated. But Cm decides whether an AOA can be reachable.

@LJQCN101 this is why G forces felt by the pilot (of constant weight) may be different from load forces (from varying wright).  GA aircraft specs "get away with" G load limits because aircraft weight does not vary much.  Really waiting for a 747, 777, C5 Galaxy pilot to "weigh in" on this subject.


text:
Why do airlines have geographical names in them?
Why do airlines name themselves for example "Cathay Pacific" or "Virgin Atlantic". Aren't they indirectly limiting themselves to always fly over "Pacific" or "Atlantic"? It would be weird if Virgin Atlantic flies over Pacific and vice versa.

It is better to do some home work before posting a question, you might get an idea, if you are still having a question then you can post it here also you need to check is there any question asked before too. Whoever Votes down it is option to write comment, but not necessarily :) you can check few of my deleted posts :)

I'm voting to close this question as off-topic because the only link it has to aviation is that it asks about names of airlines. On top of that the question is really trivial and - as other close-voters say - primarily opinion-based.

I think it's a valid question, while been asked in a too simplistic way. What about EuroAtlantic Airways, or Air Atlanta that you may spot anywhere in the world ? Or what's the point behind Indonesia/Thai Air Asia ? Trivial answers would be Air Atlanta (or Air Memphis) started operations in Atlanta (Memphis) ? Is Avianca Honduras a Colombian airline ? etc.

Air France flies all around the world,  customers are not misled by the name. Corsair has been seen at TNCM, not only in the small island of Corse on the Mediterranean Sea.

In a lot of cases it's because they started serving a specific region.
Lucky tells the story of Cathay Pacific. Virgin Atlantic was started specifically to fly from Britain across the Atlantic. Lots of US airlines started in a specific region, like Southwest. Westjet started serving the west of Canada.
It doesn't make sense to change a well-known name just because the reach of the airline is extended.

Fair enough. But why start the airline in the first place with a restricted name. Don't the founders have confidence on their brand that it'd expand.. :)

Probably because it's embarrassing to call your airline "Worldwide Airlines" when it only flies from Houston to Dallas. Also you sometimes want to communicate that your airline focusses on one specific region, that will attract people who fly in that region. And not everyone plans for their company to take over the world.

The naming of an airline completely left to the investor(founder) who is registering the airline name. Reason behind the naming for the one you are referring "Cathy Pacific" is Cathay, the ancient name given to China and Pacific because Roy Farrell (one of the founding member of airline) speculated that they would one day fly across the Pacific. More on this can be found here.
There may be a reason behind the name or may not be. I feel that it is not necessary to have a particular reason behind the airline naming or even other naming convention.

The name of a business is the business's brand name so people can identify it easily. It is totally separate from what the business does, or in the case of airlines where it flies. Its just a name and it is up to the owner to decide what the business is called and when (if ever) to change it. The names of airlines often come from the place that the airline started operations but there is no rule saying this must be so.
There is no rule stating you have to call the airline by the places it actually flies over. Generally changing names of businesses can confuse customers, so it is not done very often. I would think also that airlines are proud of their history so that's another reason not to rename just because they created a new route.


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Help identify an unknown airborne object
In the wee hours of the morning of last Saturday (July 30, 2016), while out stargazing, I saw something odd which I am unable to explain.

The object was traveling with a bearing of about 5-20° east of straight south.
The object flew nearly straight overhead, somewhat near the star Vega, sometime between 1:10-1:30AM local time (6:10-6:30AM GMT).  I was stargazing at the latitude and longitude 44.795614 N, 94.377516 W (https://goo.gl/maps/FB4yDsR8GYv).
The object was moving at a speed similar to an airplane.
The object's light blinked 3-4 times, but at a seemingly lower frequency than a typical airplane.  Also, while planes typically have a very short duration flash, this object had much longer flashes (1-2 seconds, probably), with the light being lit for about the same proportion of time as it was unlit.
I did not hear any propeller sounds, indicating that either that the object was relatively far away or that this was not a plane/helicopter.
The light also seemed brighter than a typical airplane's light, although I can't be entirely sure.  It was certainly brighter than every star in the sky.
After the 3-4 blinks, there were no more blinks (and this is on a wonderfully clear night; it's not possible that it was obscured by clouds, as I could still see the stars along the path it was flying)

From all this information, I am able to deduce that it was not a satellite, as satellites don't blink like this.  It is presumably not a typical commercial or private flight, even though there is a small airport roughly 4.5 miles north of where I was, because the lights stopped blinking, and that is presumably prohibited in nighttime flights.  I have not heard of any plane crashes nearby, which I expect I would have, had this been a plane that went down in flight.
Any ideas what I might have seen?

I apologize, but this is going to be almost impossible to answer. It could be anything from odd optical "tricks" to moon men from planet Florax. The lights could have "stopped blinking" because part of the aircraft got in the way of you seeing it. There just isn't a way to answer this factually.

Satellites don't blink (since they don't have light sources) but they can appear to blink as they move and catch the sun on solar panels etc from different angles. My guess would be an Iridium flare or a similar flash from a smaller satellite.  If you are curious, install an app on your phone that will give you the time and location of the next Iridium flare in your area (or look it up online) then watch it.  Is it what you saw?

This is a good question but it is quite difficult to answer as there is no other evidence than you testimony. You should have capture some pictures/videos and make a description having in mind all what the comments and answer suggest so that your description could have been more specific (I know, it's too late now).

Check what flights passed at that time http://www.planeflighttracker.com/2014/02/flight-history-flightradar24.html

Yeah, I know that this is a very difficult one to answer.  I was just so curious that I wanted any help that I could get figuring out what it might have been.
@RonBeyer For what it's worth, it certainly wasn't an optical trick.  The only optics involved were my glasses, but there was no visible source of optical light that my glasses could have been reflecting so brightly.

I've edited to remove reference to 'UFO'. This technically means an unidentified flying object, but it's almost always taken as synonym for 'alien spacecraft'. Without that association you are more likely to get a sensible answer.

@Simon I wasn't aware that satellites can appear to blink.  I've seen satellites before, and the brightness of this object was comparable to the ISS.  I don't know if there are any satellites that can be about as bright as the ISS (I don't think so, but I could be wrong), but the ISS was certainly not in the same part of the sky at the time, so it was not the ISS.

@ManuH I immediately turned my camera to the object and started exposing the sensor, but that was right when the lights stopped blinking :/

@DJClayworth I thought about that, but I figured that mentioning "UFO" would pique people's interest, and that given the that the StackExhange population is relatively well-educated, I figured the majority wouldn't jump to thinking aliens :P

@BenSandeen You don't need to be using an optical device to get an optical illusion. The atmosphere itself can play wonderful tricks. I've seen highway lights high in the sky reflecting off of ice crystals at high altitudes.

@RonBeyer Really?!  That's surprising.  Although I'm pretty sure this was some flying object, given that it was moving in a consistent direction with constant speed, while I was standing still.  Also, since the blinking light was so regular, that'd seem to stand against a hypothesis of atmospheric effects.  I'd love to see something like what you mention, though!

@ViktorMellgren I checked out that nifty site, and from 12:30AM to 2:00AM, the only aircraft that crossed overhead in anything remotely near the correct direction was a FedEx plane, FX137, sometime around 12:40-12:45AM.
However, it did seem like the object I saw was traveling slightly west of straight south, while this FedEx plane was traveling slightly east of straight south.  I am not entirely sure about the direction the object was traveling in, though, and I could be mistaken.  But I'm still quite skeptical.

I said Iridium, not ISS.  Iridium flares are at least as bright as the ISS, indeed most of them have the lowest magnitude of any object in the sky for a second or two.  Several other types of satellite also flare but with magnitudes quite a bit larger.

Interesting, I thought that the ISS was the brightest satellite.  When you mentioned Iridium flares, I just assumed that they were some sort of meteor shower-related thing, because iridium is an element.  I didn't realize there was also a constellation of satellites that share the same name!

Your description reminds me of seeing military aircraft practicing in-flight refueling. The blinking lights you saw might be called rendezvous lights.

My best guess is you saw a high altitude aircraft flashing its landing lights.
Landing lights serve a number of purposes. Besides illuminating the landing surface, they can also be used to signal other planes as they are so bright. To experience how bright they are, stand near the approach or departure path of a busy airport at night.
The reason for the pilots flashing the landing lights in your scenario is unknown. It could be signaling another plane on a potential collision course, or just a way of saying hello to other traffic (hey, cruising a commercial airliner is kinda bored, huh?).
Without any visual reference, judging distances on a nighty sky can be tricky. Flashing a light is a convenient way of saying "hey I'm here!" to other planes. It is likely that your judgment of the flying object's distance was also impaired by the night environment. The only reliable observation I would pick is that you did not hear any sound, which suggests the object was very far away.

But is it permitted for an aircraft to fly without any lights whatsoever?

@BenSandeen No it is not permissible for aircraft to do fly without lights on.

@BenSandeen it is possible that the navigation lights were very dim at your distance, or obscured by part of the airframe (after all they're not designed to be observed at this angle)

@kevin True, but I doubt that it would be blinking with perfect regularity, if that was the case.

@kevin Oh wait, I see what you mean; you were saying that they would never have been visible at all, and that blinking lights I saw were just the landing lights.  That seems plausible enough


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At what speeds can an airplane land?
I have read people's stories that they landed their small planes (e.g. C172) on bigger airports. They strongly recommended landing at a higher speed and without flaps as the runways are quite long, and there is traffic behind them.
Hence, if I want to land an airplane at higher than recommended landing speed (e.g. VS0):

How fast can I go?
What is the procedure to do this?
What consequences are there (good or bad)?

As a practical matter, aren't landing fees set high enough at major airports to discourage small planes from using them (among other reasons)? Would anyone want to pay those fees (plus the hazards of having heavies ahead and behind you) to routinely fly in and out of a major hub? Are we talking about doing it only out of absolute necessity?

@PhilPerry At least in the US the fees can be quite reasonable. For example the off-hours landing fee at JFK is $25 for something like a Cessna 172. (There are however a bunch of OTHER fees that can make it an unattractive option, the fuel is hideously expensive, etc.) I know a few folks who have flown into JFK and forked over the $25 (plus fuel) just to have the entry in their logbook.

@PhilPerry depends on the airport, and sometimes of course you have to. Maybe you need customs facilities and it's the only place in a wide area that offers them, or you've an appointment at the business jet terminal to drop off or pick up someone. Some flight schools associated with airlines use light aircraft to train people the procedures at their future home base. Etc. etc.

Clearly the title is missing the word "safely" :-)

@PhilPerry:  Take a look at this question

@abelenky, it reads like the tariff posted on the side of a Manhattan taxicab!

I suppose it depends on what you mean by "land" -- For our purposes I'll define landing as putting the aircraft on the ground and decelerating to taxi speed, while meeting the other requirements of a "good landing" (shiny side up; rubber side down; aircraft, pilot, and passengers in reusable condition).
How fast can I go?
Generally you want to put the wheels on the ground at (or at least very close to) the aircraft's stall speed and then decelerate to a safe taxi speed. You can certainly force the wheels onto the ground at higher speeds, but you're still an aerial vehicle at that point and you have to bleed off the excess speed to transition to a ground (taxiing) vehicle before you can leave the runway.
As a general rule of thumb your final approach speed should be about 1.3 times stall speed for your selected landing configuration so you can get down to taxi speed reasonably quickly.  Putting that into some kind of context, a normal approach speed (with full flaps) in the Piper Cherokee I fly is around ~65 knots. A no-flaps approach is ~75 knots.

Looking a little deeper, you can fly the approach as fast as you want (within reason) as long as you're comfortable doing that and confident in your ability to bleed off the extra speed with precision.
  At my home field I've been chased down final by jets often enough that I know I can maintain 85+ knots until about a half-mile final, at which point I can reliably dump the extra speed, put the wheels down in the touchdown zone, and decelerate to taxi speed in time to make a "normal" turn-off. I also know that if it seems like I will need to carry more than about 85 knots by the half-mile point I'm better off telling ATC I'll go around and land after the faster traffic because I may not be able to safely decelerate and turn off the runway with enough room for the traffic behind me to land.
  Keeping your speed up is really only helpful if you don't botch the landing.

What's the procedure for doing this?
The procedure is basically "Keep your speed up until short final" -- It's something you can practice with your CFI pretty easily.
If you elect to land without flaps the procedure is the same as the "no-flap landings" you should have done in training, and in most small aircraft that should be a non-event. Again, this is something you can practice with your CFI pretty easily, and it's a technique you should be familiar with in case your flap controls ever fail.

What are the consequences?
Well, the good part is you'll be helping out ATC and the traffic behind you: if you can keep your speed up ATC will be better able to maintain separation between you and the faster aircraft behind you, instead of having to send them around or vector / re-sequence them for spacing.
It's also fun to do this kind of thing occasionally, and helps keep your skills sharp.
The bad part is that any time you're not flying a "normal" approach you're accepting some additional level of risk. In this case you're also touching down faster, which means more energy to dissipate (hopefully through braking, but if something goes wrong you'll be dissipating that energy through impact, and as dvnrrs pointed out the energy you need to get rid of is proportional to the square of your velocity so the number goes up fast).

Remember that ultimately flying a fast final or touching down in an alternate (faster) configuration is a courtesy to ATC and the traffic you're mixing with.
If you're comfortable doing it everyone will appreciate your help, but if you aren't comfortable with it just fly a normal approach and let ATC know you are unable to fly faster -- the worst thing ATC will do is ask you to go around and re-sequence you with more space next time.

ATC should ask the traffic behind you to go around, not you. ATC's mandate is first-come, first-served (stretched a lot in practice but not that far). And you quite properly mention "accepting more risk." I would encourage readers to consider that aspect carefully.

Can it be said that at anything above stall, you're essentially flying at an altitude of 0ft agl?

@dvnrrs I agree that ATC should ask the traffic behind you to go around everything else being equal (particularly on instrument approaches). In practice I don't think I've never been asked to go around for faster traffic behind me, but I've been turned off a (long-ish) final on a visual approach to be re-sequenced behind faster traffic several times. In the hierarchy of "Safe, Orderly, Expedient" first-come first-served is a big part of "orderly", but there's a lot of wiggle room under "safe".

@CGCampbell You could definitely say that, and I would argue you're still effectively "flying" a good amount below stall speed too - your control surfaces are still at least somewhat effective while you're bleeding off speed braking on the runway. "Always treat the aircraft like it's flying until it's tied down."

Note: Much of this material, and more, is also covered in answers to the question:
Can you fly a light GA airplane into a major hub? (Didn't know that at the time I wrote this answer.)

Landing at higher than normal speed is not recommended.

Tricycle gear airplanes require a nose-high attitude on touchdown in order to ensure the main gear touch down first. The nose gear is not designed to support initial touchdown forces. In many typical small planes, forcing the plane onto the ground at too high a speed will strike the nose wheel first, risking a collapse or prop strike.
At high speed, the control surfaces and wings are still capable of producing significant aerodynamic forces. If you've forced your wheels onto the ground, you may be producing a lot of torque with the elevator, again, risking gear collapse.
Kinetic energy is proportional to the square of your velocity. And crash damage -- both to the airplane and to its passengers -- is proportional to energy. If you do collapse the gear or lose control, you're going to have a lot more energy to dissipate. And if that energy is dissipated by your body, it's going to hurt. A lot.
You might overheat your brakes, causing brake pad/rotor damage or even a fire (I'm aware of at least one instance of a Piper Cherokee catching on fire because the pilot attempted to take off with a half-stuck parking brake.)

It is true that you will sometimes be pressured by controllers at large airports to keep your speed up as much as possible on approach. It's hard for them to sequence you when you're only flying half as fast as the guys in front of and behind you. The important thing to remember is that this is their problem, not yours. There's no FAR that says you must hot dog your airplane in order to fit in with the big boys.
Here are some things you can do safely to make everyone's job easier when operating at large/busy airports:

Practice your controlled-airport/airspace proficiency.

Know, and use, standard ATC phraseology.
Listen carefully for your callsign. Don't make them repeat themseleves.
Have a plan in advance, know what you want, and make sure you communicate that to them clearly.

Have the airport diagram handy, and study it before the flight so you know where you'll be taxiing and won't mess up ground operations. Ideally you should be able to taxi on your own, but if you're not comfortable when you get your taxi instructions, request a progressive taxi.
Know your airplane and its capabilities. Fly your approach at the highest practical speed, but no faster. Know how fast you can go on a 3 mile final in order to be able to decelerate to normal short-final and touchdown speeds.

If you're not comfortable with your proficiency in these areas, consider getting some more practice before attempting a flight to a "major" airport. Or, bring a CFI along with you who can help you out and give you pointers.
The bottom line is under no circumstances should you compromise safety in order to please ATC or the airline pilot behind you. As long as you are proficient and do your best to accomodate ATC's requests within the safe capabilities of your airplane, you'll do just fine. (In fact, I've found controllers at major airports to often be very pleasant to work with.)

Nice answer (I think). +1 I was wondering whether it would be helpful to all concerned if you would simply touch down much further down the runway? (Assuming there are no intermediate veer-off points.)

@GlenTheUdderboat Most major airports have plenty of turnoffs for exactly that reason (spend less time on the runway). If not, aiming further down the runway is fine, but coordinate it with ATC first. They'll be expecting you to aim for the touchdown zone unless otherwise arranged. Also, watch out for "wrong-way" (> 90°) high-speed turnoffs. Don't use them unless arranged with ATC beforehand.

Great answer. I mentioned (in the other question about landing a small plane at a big airport) that I usually approach fast (129 knots, say), but I should add that I don't land that fast. Somewhere between short final and flare you'll come back to your usual speed, and land a bit further down the runway (which is good, as you'll be closer to the next taxiway). I'm not a stellar pilot, and found this not too hard. But remember: kinetic energy and landing distance vary (approx.) quadratically with speed, so you'll need 4x the usual distance for 2x the approach speed.

Final approach at a major hob will begin a LOT further out than at the single-strip country airport most students learn at, and mixing a 172 with the larger planes really is a significant (and expensive) issue. The cessna in the queue has everything including the glove box wide open while the 767 behind it is dancing with the Stall Demons.
However, approaching at full throttle and landing at full throttle are not the same. You have a lot less inertia and thus can slow down rather quickly. Once you pass the middle marker, pull the power back to idle, set the prop to full fine, and drop the flaps. You will decelerate rather quickly (and bob around a lot, practice somewhere first) and thus land at a better speed for your aircraft. If the next exit is a long way don't use any brakes, raise the flaps and just keep rolling at 60 kts.
I used to work at a busy skydiving center, when we went into the nearby international airport ATC recognized our aircraft and often cleared us for either a fast approach or a cutoff approach ( "Squeeze in behind the Dash-8 that's about to land and the 737 on 5-mile. Take the first exit.") Our guys made 20-30 fast-approach landings a day and could pull this off easily. The flying club got to wait.

Others have covered this subject pretty well but I will add that landing too fast will put your nosewheel down first.  The nosewheel is the weakest leg of your landing gear and if you put it down too hard you can break the nosewheel off or bend/wrinkle the firewall.  Cessna 182s are notoriously easy to damage if you slam the nose gear down.  Fixing or replacing the firewall is not an inexpensive task.

ATC is responsible for aircraft separation and they are aware of the speeds your aircraft operates at.  Land at your normal landing speed.  A large, busy airport is a bad place to try something new.

True. However, if you have a less busy, but unusually long runway in the vicinity, I'd practice a fast approach, no-flap landing and subsequently would aim to approach fast at large, busy airports.

The landing without the use of the flaps is a good and safe method of landing (touching down) at a higher speed. This causes the nose to be at the same nose-'high' attitude at a higher speed.
In high crosswind situations, I would recommend landing at higher speeds too as this reduces effect of the crosswind component.
As long as you have enough runway and don't land nosewheel first, I think it's safe to touch down at higher speed and actually safer in some situations.
Approaching at higher speed at busy airports is also safer in my opinion. If you have to go around at a busy airport and don't know your way around exactly and have to attempt another approach and feed in between two airliners again, I'd go for a faster approach and landing if you're capable of doing that.


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Why do zero gravity flights not stall?
Airbus' (A300 / A310) are being used by French companies (i.e. Novespace) that offer zero G flights.
Now the airbus seems to risk a stall at a 40 degree angle of attack (i.e.Air France 447).
In a zero g flight, they climb at 45 degrees and then nose dive at the same angle.
Why does the climb not stall the aircraft?

The angle of climb is not the same as the angle of attack.

The above comment is correct, please don't confuse Angle of Attack with climb angle (gradient).

@RonBeyer What is the difference please?

See: Can the pitch be very different from the angle of attack?.

Angle of attack: Angle between relative air flow and aircraft longitudinal axis (roughly: Angle between flight path and aircraft nose in side view. „Does it point where it goes?“). // Pitch angle: Angle between level plane and aircraft longitudinal axis (Angle between nose and horizon in side view). // The two are only the same in zero wind level flight.

@CptReynolds Ok thanks. Should I delete the question?

You’re welcome! Not sure re. deleting - it may help others with the same question? For an admin to decide!

@Cloud You are asking two questions and both have been answered. However, you don't need to delete it. Let it get closed.

I don't think the proposed duplicate is the same question at all. That question is about stalling in the zero-g phase of flight, while this question is about stalling in the climb.

The pitch angle is not the angle of attack, here's a diagram   https://qph.ec.quoracdn.net/main-qimg-361a07f4547f260fd936b17aafd7b93b-c

The aero-dynamics of a flight in reduced gravity are different than a flight operating in normal conditions. When an aircraft is experiencing zero gravity, it does not stall because the wings are not generating any lift, because the aircraft is in a state of weightlessness.
In the paper for the requirements for zero gravity flights, it is mentioned (PDF):

... zero G flights stalling conditions are different as compared to
  conventional flight maneuvers, because the plane is weightless and is,
  therefore, in no need of aerodynamical support. On the other hand, a
  minimum speed is required to execute the delicate control through the
  parabola. For this reason the stalling speed is taken as the minimum
  aircraft velocity required for effective control.

It sounds a bit like a sailing craft needs a little "way", as sailors say, to steer, to control.

But I was referring to the climb, not the ZG phase

The climb is fine, @Cloud - the airspeed and angle of attack are not likely to cause a stall. The pilot is not trying to hold the nose up and lose speed such that a stall occurs, but instead aims for a parabolic arc.


text:
What is this plane from WWII (probably French or Allied forces)?
Picture should have been taken after or during the end of World War II, probably close to Marrakech French base (but that is not sure). Can anyone tell us what these planes are? My grand father could be one of the pilots and I would like to find information on him.

It's an RAF Coastal Command Vickers Wellington, a maritime patrol variant, with a chin radome for its search radar and the nose turret removed and just greenhouse for observing.  The dark projection on top just above the cowling is a fairing for a Direction Finding loop antenna on the fuselage.  The dark shapes farther back are just dark painted areas.  Here's a shot of a similar one:

If you're sure the picture was taken near Morocco, it was probably doing sub hunting in the Mediterranean and nearby Atlantic.  Likely with 179 Squadron, based at Gibraltar.

It looks to me like the (supercharger? oil cooler?) air inlets on top of the cowlings may be significantly different (taller?) in your photo than in the photo attached to the original question.  Do you agree?  (Doesn't affect the accuracy of the answer, I'm just curious.)

Also as another side point, the boundaries of the transparent areas on the upper nose are different between the two photos (assuming L and R sides are symmetrical)  .  So clearly we have two different variants here.

I think what you are thinking of as the air scoop is the teardrop fairing on the fuselage.  The scoops themselves that are white in the pic I posted are black in the OP's pic.  So the whole dark mass is, from left to right, three elements merged into one shape: the back end of the cowl (which bulges up on the Wimpy), the engine inlet scoops, then the DF antenna fairing.  You can also see the mast for another wire antenna sticking up right behind the cockpit.  On the nose, just variations from aircraft to aircraft, as these are likely field mods or at least post production mods.

Thanks for the feedback but I don't fully agree; I think the scoops are smaller in the original pic. Just to re-iterate I think the scoops are larger in your pic, not vice versa.   I do see the black teardrop fairing of the antenna on the fuselage in both pics.

A little bit perhaps but it's impossible to tell with such a blurry pic.  In any case, they are the same type, just not the exact same airplanes.

Thanks you so much ! That's fantastic to have your help and your knowledge ! Many thanks again ! I wil try to investigate further and i will post information if i can find more things. It comes from a serie of pictures taken in Marrakech in 1948-1949 by a french army photographer, friend of my grand-father.

Following your information, I think the plane in this picture (from Wikipedia) is very close to the plane in the original picture. As we can see Gibraltar rock, it should be Squadron 179 as you told.
Thanks again!

Note that 179 was only running Wimpies until 1944, so your pic must have been taken about 1943 or 44.  Possibly the negs weren't developed until '48 and that's where your dates come from?

Yes given the new photo posted in new answer I'd say the scoops on top of cowl are slightly shorter (vertically) and somewhat longer (horizontally) in the variant featured in the original post, and also in the new answer by original poster, than in the photo in your answer.  In the OP/ new answer pics the top of the "scoop" structure seems to rise very slightly from front to rear and then start dropping, not so much so in your photo where it seems to be level horizontally and then start dropping off, w/ a shorter overall length but more height.  Just an observation; great answer here anyway.

RAF passed an order for over 200 'Wellington' heavy bombers around june 1939, this points to war being expected or wanted. This airplane has a very original fuselage construction, a Geodesic frame, shape most known from some domes . Blessings +

It's interesting how geodesic became a kind of aviation dead end.  A great way to make a compound monocoque shape if your available material is long skinny strips or sticks, but inferior to stressed skin in both efficiency and manufacturing ease (the stressed skin being both the structural material and covering).  I have plans for a homebuilt I was intending to build, call the Cygnet, that used a geodetic structure for the wings of thin wood strips to get a decently light and torsionally stiff wing. Very time consuming to make however.


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Does the FAA take programming language selection of the aircrafts' avionics as a factor when deciding the aircraft's airworthiness certificate?
It looks like many military/space/aviation instruments are programmed in Ada or Spark. Because these languages claimed and proved their safety. What if your system is not written in these languages? Will that influence FAA giving it the airworthiness certificate?

Not necessarily off topic, but you may get more people involved in the avionics industry (and thus able to answer your question) on a software engineering site instead of here.

Welcome to aviation.SE! Is this question helpful?

Software development for airborne systems is typically covered by DO-178C (C being the latest revision). When the certification authorities look at your project, they will be looking to ensure that you have met all of the objectives set out in this document, have documented processes to satisfy those objectives and evidence that you have followed them.
DO-178C does not mandate any particular language over another, it is all about process. As mentioned, using a qualified/qualifiable compilers allows you to claim credit for many of the objectives around source to object code traceability i.e. does the C code that I wrote match what the compiler output. There are cases where a compiler may optimise out certain decisions in the code depending on the optimisation settings. Developers have to understand these settings and stick within the guidelines set-out by the compiler developer.
If you don't have a qualified compiler, you will have to conduct the source-object code trace manually or use a qualified verification tool to check the output.
In addition to DO-178C there are a number of supplements including DO-332 which covers Object-Oriented programming techniques to support languages such as C++.
In short: The language doesn't matter as much as the process does.

In my experience, the programming language selected is less important than other factors such as:

the development team's experience with the language.
the complexity of the product being developed
the safety criticality of the product, which, as Gerry pointed out, can drive the selection of a certified compiler

That last bullet typically drives the discussion to the selection of the compiler(s) to be used, especially with DAL A software. Having an FAA qualified compiler; e.g., Greenhills or Wind River, will greatly simplify the verification effort.

Cannot believe it, it really does. So a certified compiler means language selection. And the greenhills and windriver you mentioned must be costive propritery compilers, I must guess

Yes, Wind River and Greenhills development tools (which include a compiler) are not cheap. But trying to certify your code using a non-qualified compiler means a lot more work for you (schedule impact) with no guarantees and potentially even more expenses. And they also keep their tools up to date as the target processors evolve. Given that avionics can have a service life of 20 years or more there will be the need to update the products as components become obsolete. Having these tools means being able to recompile the old source code for the new targets with minimal effort.

@Gerry I've seen validation on some lower assurance level, and my impression is that it involved quite a bit of cargo cult and missing the point, because nobody really understood what is required. People who really understand and can do the validations efficiently are few and far between, so not needing to find someone is always welcome. On the other hand, Space-X was apparently able to certify a hybrid (browser-based) UI for space flight, so competent people clearly can get almost any technology certified.

@JanHudec I won't disagree with you. In the SW development world, aerospace is a niche business. Working with the FAA, NASA and DoD has it's challenges. If you have the right people leading the effort, a good organization with solid processes and procedures in place, and regular communication with your certification authority it can all go relatively smooth. If not, it can be a real challenge. I've seen some pretty "creative"  non-traditional solutions over the years get certified. It mostly comes down to money and your tolerance for risk (to the program).


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Why did some Spitfire variants have their wings clipped?
Some Spitfire variants have clipped wingtips instead of the round, elliptical wingtip. The reason for this is to increase the roll rate and low-altitude performance. My question is: How would clipping the wings of an aircraft increase its low altitude performance?

It would increase the roll rate, and it would increase the maximum possible airspeed at lower altitudes.  Generally speaking, decreasing the wing loading doesn't help to maximize the achievable airspeed unless an aircraft is near its service ceiling.  At low altitudes, increasing the wing loading by reducing the wing area often increases the maximum achievable airspeed, by reducing profile drag.

As Pierre Henri Clostermann says in his "Grand Cirque":

Spitfire V: nickname:clipped,cropped,clapped

Clipped = tip of clipped wings

Advantage:increased speed and lateral maneuverability. wings reduced by about one meter.
Disadvantages: this reduces the bearing surface and increases the marginal vortices

cropped

the RR Merlin's compressor rotates faster, and increases the intake pressure ...
This has the effect of increasing the amount of air entering the engine, while the displacement remains the same.
The Merlin of these series (around 40) gives around 1,650 CV at ground level, while the XX series (approx.) Of the classic Spitfire Mk.V give only 1,200 (below 10 000m)
The downside is that is that an inflated engine is less reliable and it lasts less time

Other disadvantages: that at 3500 m=50 cv and the guns have only 60
  shells each against 145 in the Spitfire IX!

Clapped=literally rotten

personal appreciation of the time ... of the pilots !!!

@J Lopez Can have more info here:quora.com/Why-did-some-Spitfires-have-clipped-wings-in-WW2

It apparently increased the roll rate of the aircraft and made a more optimal design for low altitude operations and ‘air-to-mud’ work happening more and more near the end of the war.  The cropped wing Spits were often paired with superchargers equipped with cropped impellers optimized for lower altitude flight, though this was not always the case.  It also improved manufacturability over elliptical wing Spits.

Yes, I have heard that the elliptical wing of the spitfire required more skill to make than other types of wings.


text:
FAA to TC conversion
I am trying to convert my FAA ATPL to a Canadian ATPL. However I need to do an IPC and a Bi-annual flight review. Does anyone know of  anywhere/anyone in Canada  that can do this? I need to do it here in Canada.

Does this thread help?


text:
Do fighter pilots have to manually input the ordnance they have loaded on the aircraft?
When ordinance is loaded onto a fighter or bomber, does the system automatically know what ordnance it has? Or does the pilot have to manually input for each pylon?

On the B-52G and H models (at least in the 80s when I worked on the simulator) weapon loading was part of the data read into the Offensive Avionics System preflight, from a digital tape cartridge.

MISSION DATA LOAD

The FMS provides a method for the user to load a sortie and a mission data file from the DTS. Up to eight
sorties can be resident on a DTC. Each sortie contains
up to nine B-52 missions. Mission data consist of a set
of up to 99 pre-planned destinations, 99 fixpoints, 42
OAPs and data required by the weapon SMOs for release of weapons at one or more of the destinations.
The resident sortie or mission, if any, can be viewed
on the Mission Supervision Display, CF-8, or the Mission Data Load Display, CF-81. To load a sortie and
mission see Mission Supervision Display this section.

SMO LOAD

FMS allows the operator to load multiple Stores Management Overlays (SMO) into memory and select one
of the loaded SMO to be the Primary SMO. For each
possible weapon location one SMO can be loaded. The
CF-62 display shows all the SMO available from the
DTS, indicates which (if any) of these SMO are already loaded, indicates which SMO (if any) is the primary SMO, allows the operator to modify what SMO
are loaded, what location(s) each SMO is to control,
and allows the operator to select a SMO to be the primary SMO. To load SMOs and designate a primary
SMO see SMO Load Menu (CF-62) this section.

Acronymology:

DTC Digital Tape Cartridge
DTS Digital Tape System
FMS Flight Management Software
OAP Offset Aimpoint
SMO Store Management Overlay

Source: Radar Navigator’s/Navigator’s
Manual USAF SERIES B-52H AIRCRAFT, page 1-134

This depends on the aircraft in question, but current F-16 and above get programmed with whatever load they are carrying. The pilot does not have to do it manually.
There is a Common Central Interface Unit (CCIU) the ground crew programs when they load the aircraft.
https://www.centcom.mil/MEDIA/igphoto/2001694833/

Just to clarify - this still means that someone manually inputs the loadout either via computer or data cartrige right? The plane won't "autodetect" what's hanging on the pylons?

What can be the reasons of not using "smart" ordnance with a basic identification feature (mechanical, optical, data exchange, etc). A printer knows the model of ink cartridge inserted, a camera the lens used, an oscilloscope the probes connected, a computer the USB device plugged, etc? Why not using this plug and play model for ordnance? Lack of standardization?

@Mavrik - Some munitions can tell the aircraft what they are, some cannot. AIM-9 vs AIM-120 on a wingtip launcher, it can tell the jet. MK-82 (500lb) vs MK-84 (2000lb) dumb bomb...there is no data connection. The aircraft can know "something" is there. But not what.

@mins - Not everything is "smart". A Triple Ejector Rack (TER), with 3x MK-82 dumb bombs looks, to the jet, exactly the same as 3x 25lb BDU-33 practice bombs.

Thanks. Related: MIL-STD-1760 Aircraft/Store Electrical Interconnection System

@mins I could see reliability being an issue. If somehow the avionics detect no munitions or incorrect munitions, then it may be impossible to deploy them. Also the same munitions may be loaded onto aircraft with very different avionics packages from very different manufacturers. Of course new contracts could specify standards, but it would take a few decades for enough aircraft and munitions to be refreshed to make the standards actually standard. Which is not to say it's not a good idea. Maybe it's just not been seen as a good enough idea for change to happen.

@ToddWilcox see also Red Storm Rising where an maritime patrol aircraft is scrambled in a hurry and missed a config detail, making the weapon un-fireable, and were unable to deliver the killing blow to their prey.  I'm sure Clancy based that on real world experiences… So manual systems are not 100% reliable either.  Something like the BDU-82 vs 84 could be simply magnets on the launch bracket.  Cheap and simple, like how cassette tapes detected chrome or metal.

"What can be the reasons of not using "smart" ordnance with a basic identification feature (mechanical, optical, data exchange, etc)"   Easy to answer. Military stuff has to be reliable.

Of course, the fact that much of the weapons technology (and outright ordnance) dates back from 1980s also makes a difference.

@Mavrik - Even earlier. Current "smart bombs" are mostly Vietnam era bombs, with a guidance unit on the front, and steerable fins on the back. The GBU-12 Paveway II is literally that, a 500lb Mk-82 general purpose bomb, with bolted on "smarts". https://en.wikipedia.org/wiki/GBU-12_Paveway_II

@ToddWilcox It wouldn't be hard to retrofit existing ordnance and aircraft with identification systems.  The sophisticated stuff needs a data connection anyway, that leaves just the dumb bombs and the laser guide bombs (dumb bombs with a laser seeker) to identify.  That's not a lot of bits, a strip of metal with/without magnets at certain locations would do fine.

@Fattie So long as the pilot can override the detection it would be more reliable than not having it.  And if you put decent error detection in your encoding it would be pretty hard to have a weapon come up misidentified.  Malfunctions would be along the lines of "unknown store", the pilot would know what he should be carrying.

@Loren Pechtel - There is little need to make mods to have ALL of the munitions self identify. There is a large body of information that various segments of the ground crew have to preload anyway. IFF code, radio freqs, etc, etc. The weapons loadout is just one more

@LorenPechtel "It wouldn't be hard to retrofit existing ordnance and aircraft"... a mere trillion dollars and decade of effort!

@fectin Depends on how much they manage to milk it.  I'm saying it would technically not be that hard, it would just be a small piece fastened to the bomb and the reader on the airplane.  An easy retrofit, nothing needs to be replaced.

@LorenPechtel if you don't know what drives this to be hard, you are probably not ready to have opinions on whether things are easy.

@fectin I agree that from a standpoint of actually getting it done the bureaucracy would make this very hard.  That's a political problem, though, not a technical one.


text:
How were compasses in early interwar planes safeguarded against interference from flight?
I understand during the early days of flight that compasses were regarded as extremely unreliable and unfit for even basic navigation, but I'm unsure as to what caused this unreliability and what the first countermeasures against it were.

Does this answer your question? How do you calibrate the compass of an aircraft on a compass rose?

Don't see that as a duplicate, since this question has a historical component to it and asks about not just the solution (the compass swing) but also the causes of the unreliability.  The info in the linked question is a good addition here, but it isn't really a full answer to everything being asked, IMHO.  Voting not to close.

I do not think magnetic compasses are considered very good navigational aides even these days. The term for the magnetic compass in an airplane in my native language would loose translate into a "screw compass", because if you have to rely on it, you're screwed...

The unreliability is caused by the nearness of several big bits of magnetic material, chiefly an engine, and some electrical equipment. The countermeasures are something called "swinging the compass". The same fix has been used historically on boats since they started being made of metal.
In essence it involves adjusting "compensators" which are pieces of magnetic material placed near the compass and which cause it to swing by a few degrees. You point the aircraft in all the different compass directions and make the adjustments in order to minimize the deviation of the compass from an accurate reading throughout all directions. This is done in a "standard configuration" of different electrical equipment being on or off.
Once you have minimized the difference between actual directions and what the compass reads you then make up a "deviation card" which is placed near the compass and which the pilot can use to get the correct magnetic heading from the compass reading.
There is an additional unreliability caused by the aircraft's motion. As an aircraft pitches and rolls that movement causes the compass to deviate from an accurate reading. This would happen more in early planes than in more modern ones. This problem was fixed by the invention of the gyro compass or "Direction indicator", which maintains a constant direction and is not subject to the aircraft pitch and roll. However the DI does drift, and so needs to be regularly checked to ensure it aligns with the compass, something you do during level flight to minimize the compass errors.
Both of these mitigations are in use today.

One common method was to move the guts of the compass out to a wingtip, far away from the engine block and the electrical system, and then electrically link it to a remote reading dial in the cockpit. This was called a flux gate compass, which does not use a swinging needle to detect the direction of the earth's magnetic field and hence does not dance around in rough air.

The Wikipedia page pointed to this Aviation Week article, which makes the flux gate compass public knowledge in 1943 (though calls it the result of "seven years' study"). The question specified "early interwar"... was there an earlier version of the fluxgate compass in use?


text:
Is it better to fly faster or slower through turbulent air?
If you had to pass through turbulent air, and your only goal was to give the smoothest ride possible to your passengers, would you push that throttle or would you reduce the throttle, or would it be the same either way?

The ride is better slower, for the same reason that speed bumps work for cars: the more rapidly you transition from an updraft to a downdraft to an updraft, the greater the felt change in acceleration, or "jerk". Or, put simply, the worse the ride.
The limit there is that you don't want to go too slow in turbulence for other non-ride-related reasons, such as wanting to keep a comfortable margin above low-speed buffet.  Large aircraft will generally have a turbulence-penetration airspeed published, and that speed is typically somewhat slower than normal cruising speeds.

However at infinitesimal high speed the duration of the bump is infinitesimal small giving a smooth ride without long travel times :D


text:
Why do dihedral wings increase induced drag?
I read somewhere before that the effect of the dihedral wing is similar to the swept wing so dihedral wing increase wingtip loading and increase induced drag
Can anyone tell me how physically this is possible ?

related: How do anhedral and dihedral affect the efficiency of a wing?

https://www.researchgate.net/publication/268564853_Induced_Drag_of_High-Aspect_Ratio_Wings#pf7  https://aviation.stackexchange.com/users/12589/mike-sowsun

There is some academic writing about this phenomenon.  The most articulate explanation I have read comes from a paper Induced Drag and Winglets by R. Eppler, Universität Stuttgart, which was presented at the XXIV OSTIV Congress in 1995.
Section 4.2:

Winglets and other forms of wing tips with dihedral increase not only
the effective span, but also the wetted area of the wing.  Although
the induced drag is considered to be completely independent of the
viscous drag, for a correct comparison of different wings it is
necessary to add to the induced drag that part of the viscous drag
that is due to the difference in wetted area.

It's an interesting read and the section provides illustrative formulas (16) through (21) for those mathematically inclined.
A grainier "old school" PDF is available at this link from Simon Fraser University.
Eppler has written several books and scholarly articles on airfoil design.

this is about wingtip not whole wing


text:
What are the holes on the top side of the canard of Eurofighter Typhoon for?
The Eurofighter Canard has some holes on top side. What are these holes for?
?

They aren't holes they're flush screw heads.
The fasteners have some form of recess for the screwdriving tool, like Phillips or tri-wing or similar, and it depends on the lighting whether or not the recesses are emphasized. In the bottom shot the light source from directly above emphases shadows in the screw head recesses. Visibility also depends on the paint coating and how much the paint fills the screw heads.

Thanks, I appreciate answer, to me looks like some holes but must  be flush screw heads, some Eurofighter-typhoon don't have them , anyway ,another ones have it , but not in the  same pattern! Just a curious thing to me.

The fasteners have some form of recess for the screwdriving tool, like phillips or tri-wing or similar, and it depends on the lighting whether or not the recesses are emphasized.  In the bottom shot the light source from directly above emphases shadows in the screw head recesses.  It also depends on the paint coating and how much the paint fills the screw heads.

They are indeed fasteners joining the actuators to the canard, as visibile for example in this cutaway.


text:
Why descend after a single engine failure in an Airbus?
The procedure says to descend to lrc ceiling. But, why do we need to descend?
The aircraft is still able to maintain speed even at higher altitudes,
at FL300, in FS2020, it was maintaining around 215-225 knots speed with N1 around 89 percent.
When I descended to FL150, though it is able to maintain 300 knots, power is still around same.
So why descend?

What do the real world performance charts say? Maybe the A320 in the flight simulator does not have accurate performance (especially in non-normal situations).

An Airbus can not maintain FL300 on one engine. Your simulation might be flawed, but my guess is you didn’t wait long enough for the airspeed to decrease. If you did, you would probably find the max altitude on one engine would be about FL200.

Beyond the fact that FS2020 is not a suitable mean of testing real aircraft performance. As you have written: "to lrc" i.e. Long Range Cruise. The docs don't imply that the aircraft isn't able to maintain FL300, but that descending will improve the range which is useful in case of one engine failure.

What I really want to know is that why we need to descend... I tired it in fenix and it seems to be holding speed... people told that the aircraft may not be able to maintain speed but thats not the case and as i think the simulation is right

so it will be nice if someone can give a correct and accurate explanation of real reason required to descend,.. thanks much

@757toga -- my thought was more in terms of a slower descent rate versus a faster descent rate-- ( re "So maybe now we need another question about what is the most efficient way to descend to the altitude that will provide the best single-engine range?")

@757toga you went into the other strategies, but here i'm asking for a standard situation where there is no mountains/etops... simply what is the advantage for that situation.. be particular pls thanks...

from your answer it seems it's done only to increase endurance, is it ?

correct me if i'm wrong

FenixSim is WRONG. A real Airbus A320 can NOT maintain FL300 on one engine. That is the reason for the descent.

@quietflyer the most efficient single engine descent is included in QRH performance data and is called "driftdown" speed. Driftdown is basically max L/D with one engine inop and the other at max cont thrust.

Your simulation is almost certainly flawed. For example, an Airbus A320 that loses an engine at Fl330 must descend. There is the single-engine ceiling at which a plane can maintain speed and altitude efficiently. If you want to maintain altitude, then you must sacrifice speed. If you want to maintain speed, then you must sacrifice altitude. If you want to do both simultaneously, descend.
Summarised from here: Mentour Pilot's video on this topic